1. Technical Field
The present invention relates to a piezoelectric element which includes a first electrode, a piezoelectric layer, and a second electrode, and a piezoelectric element applied device which includes the piezoelectric element.
2. Related Art
Generally, a piezoelectric element includes a piezoelectric layer and two electrodes. The piezoelectric layer has electromechanical conversion characteristics. The piezoelectric layer is interposed between the two electrodes. A device (piezoelectric element applied device) which uses such a piezoelectric element as a driving source has recently been actively developed. As one of the piezoelectric element applied devices, for example, a liquid ejecting head represented by an ink jet recording head, a MEMS element represented by a piezoelectric MEMS element, an ultrasonic measurement device represented by an ultrasonic sensor and the like, and a piezoelectric actuator device are provided.
As a material (piezoelectric material) of a piezoelectric layer of a piezoelectric element, lead zirconate titanate (PZT) is known. However, from a viewpoint of reducing an environmental load, a non-lead-based piezoelectric material in which the content of lead is suppressed has been developed. As one of such non-lead-based piezoelectric materials, for example, as disclosed in JP-A-2011-03537 or in Yiping Guo et al. Appl. Phys. Lett. 85, 4121 (2004), potassium sodium niobate (KNN; (K, Na)NbO3) is proposed (see JP-A-2011-03537). JP-A-2011-03537 discloses that the crystal structure of KNN; (K, Na)NbO3 preferably has a phase boundary between a pseudo-cubic crystal and an orthorhombic crystal.
However, in a case where the crystal structure is approximately pseudo-cubic, the crystal structure is unstable in terms of energy, and thus a large displacement amount is easily obtained with a small amount of energy. However, because the crystal structure has a shape which is close to a cubic crystal which does not indicate ferroelectric properties, in a case where a large amount of energy is applied to the crystal, large displacement is structurally difficult to occur. Thus, a KNN thin film which realizes improvement of piezoelectric characteristics is required.
Such a problem is not limited to a piezoelectric element used in a piezoelectric actuator which is mounted in a liquid ejecting head represented by an ink jet recording head, and similarly also occurs in a piezoelectric element used in other piezoelectric element applied devices.